Timsina, J., Panaullah, G.M., Saleque, M.A., Ishaque, M., Pathan, A.B.M.B.U., Tisdale, S.L., Nelson, W.L., Beaton, J.D. and Halvlin, J.LO. (1993) Soil Fertility and Fertilizers. 5th Edition, Prentice Hall, Upper Saddle River. - References - Scientific Research Publishing